JP2551062B2 - Rear wheel steering system for front and rear wheel steering vehicles - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a front and rear wheel steering vehicle that steers rear wheels in conjunction with steering of front wheels.

(Prior Art) As a first prior art, as shown in, for example, JP-A-55-91458, JP-A-60-15052 and JP-A-60-16674, front wheel steering is performed. Mechanical displacement proportional to the amount is transmitted from the front wheel steering mechanism to the rear wheel side through a mechanical transmission mechanism such as a link, chain or cable,
It is known that the rear wheels are steered by the mechanical displacement.

A second conventional technique is, for example, Japanese Patent Laid-Open No. 605-1.
As disclosed in Japanese Patent No. 63770 and Japanese Patent Laid-Open No. 60-259571, the mechanical connection between the front wheel steering mechanism and the rear wheel steering mechanism is abolished, and the vehicle speed, yaw rate, etc. are electrically detected and It is also known that the rear wheel steering mechanism is electrically controlled based on the detection result to steer the rear wheels.

Further, as a third conventional technique, for example, Japanese Patent Laid-Open No. 60-
As disclosed in Japanese Patent No. 161262, first and second hydraulic cylinders for driving a pair of lateral rods extended from a wheel support are provided, and each oil chamber of a power cylinder for assisting steering of front wheels is provided. The hydraulic pressure applied is the first
And the respective oil chambers of the second hydraulic cylinder, and the first hydraulic cylinder steers the rear wheels within the range of the small steering angle,
Further, there is also known one in which the rear wheel is steered to a large steering angle by the second hydraulic cylinder.

(Problems to be Solved by the Invention) However, in the above-mentioned first conventional technique, an error is included in the steering of the rear wheels due to a mechanical error due to a clearance in the transmission mechanism, a change over time, and the like. It is not suitable for delicate steering control of the rear wheels with a small steering angle.

Further, in the second prior art, since the front wheel steering mechanism and the rear wheel steering mechanism are completely separated, the rear wheels are steered to a large steering angle independently of the front wheels due to an abnormality in the electric control circuit or the like. As a result, the controllability of the vehicle may deteriorate. Although the steering of the rear wheels can be stopped due to the abnormality, the steering of the rear wheels is always stopped when an electrical abnormality is detected, and the function as a front and rear wheel steering vehicle is fully exerted. There is also the problem that it is not done.

Further, in the third conventional technique, two hydraulic cylinders are required to steer the rear wheels, which complicates the mechanism of the rear wheel steering device. Further, both hydraulic cylinders are connected to the same hydraulic system, and if an abnormality occurs in this hydraulic system, the steering function of the rear wheels is completely lost.

The present invention has been made to address the above problems,
Its purpose is to provide a rear wheel steering system for front and rear wheel steering vehicles that solves the above-mentioned problems such as delicate steering controllability of the rear wheels due to the small steering angle, safety, complexity of functions, and functions as a front and rear wheel steering vehicle. To provide.

(Means for Solving Problems) In order to achieve the above-mentioned object, a structural feature of the present invention is to provide a power cylinder that generates a steering force for steering the rear wheels by supplying and discharging hydraulic oil, and an input. A control valve that controls the supply and discharge of hydraulic oil to and from the power cylinder according to the displacement of the member to control the steering of the rear wheels in proportion to the amount of displacement of the input member from the neutral position, and the front wheel connected to the front wheel steering mechanism at one end. The transmission mechanism that transmits mechanical displacement proportional to the steering amount of the front wheel to the other end in conjunction with the steering of the front wheel and the mechanical displacement that is connected to the other end of the transmission mechanism and transmitted by the transmission mechanism are input. Drive mechanism for largely displacing the input member of the control valve in accordance with the mechanical displacement within a steering angle range of a front wheel or more, and an electric actuator electrically driven to displace the input member of the control valve within a small range. And the car And an electric control circuit for driving and controlling the electric actuator in accordance with both traveling states.

(Operation and Effect of the Invention) In the present invention configured as described above, when the front wheels are steered, mechanical displacement proportional to the steering amount of the front wheels is transmitted to the drive mechanism via the transmission mechanism. When the steering angle of the front wheels is small, the drive mechanism does not displace the input member of the control valve, so the rear wheels are not steered directly in relation to the steering of the front wheels. On the other hand, the electric control circuit drives and controls the electric actuator according to the running state of the vehicle, and the actuator displaces the input member of the control valve within a small range to control the supply and discharge of hydraulic oil to and from the power cylinder. Is steered by supplying and discharging hydraulic oil to and from the cylinder. In this case, since the electric control circuit and the electric actuator can accurately control the input member of the control valve, for example, when the vehicle is traveling at high speed, the rear wheels are delicately steered in the same phase as the front wheels to stabilize the traveling stability of the vehicle. Can be good.

Further, when the front wheels are steered to a large steering angle, the drive mechanism largely displaces the input member of the control valve in accordance with the mechanical displacement transmitted through the transmission mechanism, and the power cylinder corresponding to the displacement of the input member. The rear wheels are steered by supplying / discharging hydraulic oil to / from. In this case, since the control valve is mechanically connected via the transmission mechanism and the drive mechanism, the rear wheels are not steered to a large steering angle regardless of the front wheels, and the stability of the vehicle is ensured. To be done. Further, since the transmission mechanism and the drive mechanism are used to steer the rear wheels to a large steering angle, the error rate does not become so large even if there is a displacement error due to the transmission mechanism and the drive mechanism. Then, for example, when the vehicle is traveling at a low speed, the rear wheels can be steered to a large steering angle in an opposite phase to the front wheels to improve the small turning performance of the vehicle.

Further, according to the present invention, the input member of the control valve is displaced by both the drive mechanism and the electric actuator, and the rear wheel and the mechanical control system are electrically connected to each other by using the single control valve and the power cylinder. Since the steering control is realized by a simple control system, a mechanism for steering the rear wheels can be easily configured. Further, according to the present invention, since the steering control of the two systems is independent up to the preceding stage of the control valve,
Even if an abnormality occurs in the electric control circuit or the like, the steering of the rear wheels is ensured by the control of the transmission function and the drive mechanism side, and the rear wheel steering function of the vehicle is not lost at all.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the entire front and rear wheel steering vehicle according to the present invention. The front and rear wheel steering vehicle includes a front and rear steering mechanism A that steers the left and right front wheels FW1 and FW2, and a rear wheel steering device B that steers the left and right rear wheels RW1 and RW2.

The front wheel steering mechanism A has a steering shaft 12 to which a steering handle 11 is fixed at the upper end. The steering shaft 12 includes a pinion 13 fixed to the lower end of the coaxial 12, a relay rod 14 having a rack portion 14a meshing with the pinion 13, left and right tie rods 15a and 15b and left and right knuckle arms 16a and 16b connected to both ends of the rod 14. The left and right front wheels FW1, FW2 are connected to the left and right front wheels FW1, FW2 according to the turning of the steering shaft 12 accompanying the turning of the steering wheel 11.
FW2 is steered. A control valve 17 is attached to the lower portion of the steering shaft 12, and the control valve 17 allows the hydraulic oil from a hydraulic pump 21 driven by an engine 18 to actuate the power cylinder 22 according to the steering torque acting on the steering shaft 12.
The hydraulic oil is supplied to one of the oil chambers and discharged from the other oil chamber of the cylinder 22 to the reservoir 23. Power cylinder
22 is attached to the relay rod 14, and drives the relay rod 14 according to the supply and discharge of the hydraulic oil to assist the steering of the left and right front wheels FW1, FW2.

The rear wheel steering device B has a relay rod 31 as a steering link mechanism that connects the left and right rear wheels RW1 and RW2 in a steerable manner. The relay rod 31 is a housing supported by the vehicle body.
The tie rods 32a, 33b and the left and right knuckle arms 34 are supported by the shaft 32 so as to be displaceable in the axial direction.
The left and right rear wheels RW1 and RW2 are connected via a and 34b, and the left and right rear wheels RW1 and RW2 are steered according to axial displacement. The relay rod 31 is connected to the output shaft 36a of the control valve 36 via the pinion 35 at the rack portion 31a provided integrally with the rod 31 and has a piston fixed to the rod 31 and is housed in the housing 32. It is adapted to be driven by the formed power cylinder 37. The control valve 36, in accordance with the torque acting on the output shaft 36a and the input shaft 36b of the valve 36, supplies the hydraulic oil from the hydraulic pump 38 driven by the engine 18 to the power cylinder similarly to the hydraulic pump 21 described above.
The oil is supplied to one of the oil chambers 37, and the working oil from the other oil chamber of the cylinder 37 is discharged to the reverber 23.

A planetary gear mechanism 41 as a driving force transmission mechanism is connected to the input shaft 36b of the control valve 36.
As shown in FIG. 2, the sun gear 41a and the ring gear 41b
And planetary gears 41c, 41c. The sun gear 41a is rotationally driven by the first drive means, and the ring gear 41b
Are driven by the second drive means.
A sector gear 41b1 and a step portion 41b2 are formed on the outer periphery of the ring gear 41b, and the rotation of the ring gear 41b accompanying the input from the sector gear 41b1 causes the step portion 41b2 and the housing of the planetary gear mechanism 41 (not shown). (4) is fixed within a predetermined small range by engagement with the protrusion 41d fixed to (4). The carrier of the planetary gear 41c is connected to the input shaft 36b of the control valve 36, and the revolution of the planetary gear 41c due to the rotation of the sun gear 41a by the first driving means and the rotation of the ring gear 41b by the second driving means is the first and the second. It is adapted to be input to the input shaft 36b as a composite input by the second drive means.

The first driving means converts the displacement of the relay rod 14 in the front wheel steering mechanism A transmitted by the push-pull cable 42 formed of a non-stretchable flexible material by the cam mechanism to drive the sun gear 41a, Left and right rear wheels RW1, RW2 to left and right front wheels FW1,
The steering angle is opposite to FW2 and the steering angle is relatively large. The cable 42 is connected to the relay rod 14 at its front end via a link 43 and a crank arm 44,
The cable guides 45a, 45b, 45c are provided on the vehicle body, and extend rearward of the vehicle body. The crank arm 44 is rotatably supported by a support 46 fixed to the vehicle body.

The rear end of the cable 42 is a cam member that constitutes the cam mechanism.
The cam member 47 is supported by a support body 51 fixed to the vehicle body via rollers 48, 48 and is connected to the cable 42.
It can be displaced in the front-rear direction of the vehicle body according to the push-pull operation of. The rack bar 52 is provided on the cam surface 47a of the cam member 47.
A rotatably assembled copying roller 53 is engaged with one end of the rack bar 52, and the rack bar 52 is displaced in the axial direction according to the displacement of the cam member 47. In such a case, the displacement characteristic of the rack bar 52 is determined by the shape of the cam surface 47a. As shown in the characteristic diagram of FIG. 3, the displacement characteristic is such that the left and right front wheels FW1, FW2 are in a substantially neutral state. When 47 is near the neutral position (state of FIG. 1), the rack bar 52 is maintained at the neutral position, and when the cam member 47 is displaced forward (or rearward), the rack bar 52 moves upward in FIG. It is formed so as to be displaced (or downward). Also, the rack bar 52 has a spring 54
Thus, the copying roller 53 is urged so as to always contact the cam surface 47a. A pinion 55a fixed to a pinion shaft 55 meshes with the rack bar 52, and the pinion shaft 55 is connected to a rotary shaft of a sun gear 41a as shown in FIG.

The second drive means electrically detects the running state of the vehicle by various sensors and drives the ring gear 41b according to the detection result to compare the left and right rear wheels RW1 and RW2 in phase with the left and right front wheels FW1 and FW2. It steers within a relatively small steering angle. In this embodiment, the vehicle has a front wheel steering angle sensor 61, a vehicle speed sensor 62, a yaw rate sensor 63, and a rear wheel steering angle sensor 64 as various sensors. The front wheel steering angle sensor 61 is attached to the steering shaft 12, detects the steering angle δf of the left and right front wheels FW1 and FW2 by measuring the rotation angle of the coaxial shaft 12, and outputs a detection signal representing the same steering angle δf. The vehicle speed sensor 62 detects the vehicle speed V by measuring the number of revolutions of the output shaft of the transmission or the wheels, and outputs a detection signal indicating the vehicle speed V. The yaw rate sensor 63 is mounted on the vehicle body, detects the rotational angular velocity of the vehicle body, that is, the yaw rate Y, and outputs a detection signal representing the yaw rate Y. The rear wheel steering angle sensor 64 is assembled to the relay rod 31, and the displacement of the rod 31 is measured to detect the steering angle δr of the left and right rear wheels RW1 and RW2 to detect the steering angle δr.
Is output.

An electric control circuit 65 composed of a microcomputer or the like is connected to these various sensors 61, 62, 63, 64. The electric control circuit 65 calculates a target target rear wheel steering angle δr * based on the front wheel steering angle δf detected by the front wheel steering angle sensor 61, the vehicle speed sensor 62 and the yaw rate sensor 63, the vehicle speed V and the yaw rate Y, and A difference signal corresponding to the difference between the target rear wheel steering angle δr * and the rear wheel steering angle δr detected by the rear wheel steering angle sensor 64 is output to the electric motor 66, and the steering angles of the left and right rear wheels RW1, RW2 are changed. Target rear wheel steering angle δ
The rotation of the electric motor 66 is controlled so as to be r *. In such a case, the target rear wheel steering angle δr * is calculated by executing the following calculation, for example.

δr * = K ₁ (V) ・ δf + K ₂ (V) ・ δf / δt + K ₃ (V) ・ Y Note that the steering angle ratio coefficients K ₁ (V), K ₂ (V), K ₃ (V) are Fourth
As shown in the figure, the electric control circuit 65 is a variable that is set according to the change in the vehicle speed V and is set so as to steer the left and right rear wheels RW1, RW2 in phase with the left and right front wheels FW1, FW2.
It is stored in the form of a table inside.

The rotating shaft 66a of the electric motor 66 penetrates into the planetary gear mechanism 41, and as shown in FIG. 2, a worm gear 67 fixed to the tip of the coaxial 66a meshes with the sector gear 41b of the ring gear 41b.

Further, the rear wheel steering device B has a spring 71 through which the relay rod 31 penetrates in order to bias the left and right rear wheels RW1 and RW2 to a neutral state. The spring 71 is supported at its both ends by left and right retainers 72a, 72b slidably mounted on the relay rod 31. Retainers 72a and 72b are relay rods 31
Left and right stopper members 73a, 73a,
73b prohibits their outward displacement with respect to the relay rod 31, and the left and right stopper members 74a, 74b fixed on the inner circumference of the housing 32 prohibit their outward displacement with respect to the housing 32. It has become. The left and right stopper members 73a, 73b and the left and right stopper members 74a, 74b are arranged to face each other while the relay rod 31 is in the neutral position.

In the rear wheel steering system B configured as described above, the cable 42 is bendable and does not use a connecting member that linearly extends from the front part to the rear part of the vehicle body.
The mountability of the rear wheel steering device B on the vehicle is improved.

Next, the operation of the embodiment configured as described above will be described. First, a case where the left and right front wheels FW1 and FW2 are steered to a large steering angle will be described. When the steering handle 11 is largely rotated, the rotation is transmitted to the relay rod 14 via the steering shaft 12, and the rod 14 is largely displaced while being assisted by the power cylinder 22 to steer the left and right front wheels FW1 and FW2. The steering wheel 11 is steered at a large steering angle in the turning direction.

At the same time, the displacement of the relay rod 14 is linked to the link 4
3, cam member 4 via crank arm 44 and cable 44
It is transmitted to 7. In this case, if the left and right front wheels FW1, FW2 are steered to the right, the relay rod 14 is displaced to the left, and the cam member 47 is pulled by the cable 42 and displaced to the front. Due to the displacement of the cam member 47, the rack bar 52 is displaced upward in FIG. 1 to rotate the pinion shaft 55 leftward, so that the sun gear 41a also rotates leftward and the planetary gears 41c, 41c revolve leftward. . In this case, since the displacement amount of the relay rod 14 in the front wheel steering mechanism A is large, the rotation amount of the sun gear 41a is large, whereas the rotation amount of the ring gear 41b by the electric motor 66 is small and the ring gear 41a is small as described later. The rotation amount of 41b is
The ring gear 41b
It can be considered that the rotation of is almost stopped. By the revolution of the planetary gears 41c, 41c, the input shaft 3 of the control valve 36
6b also rotates to the left, and this rotation is transmitted to the relay rod 31 via the output shaft 36a, and the rod 31 is driven to the right while being driven by the power cylinder 37 whose supply and discharge of hydraulic oil is controlled by the control valve 36. Displace relatively large. As a result, the left and right rear wheels RW1, RW2 are in the left direction, that is, the left and right front wheels FW1, F.
Steering is relatively large in opposite phase to W2. On the other hand, if the left and right front wheels FW1 and FW2 are steered to the left, the relay rod 1
4 is displaced rightward, and the cam member 47 is pushed by the cable 42 and displaced rearward. Due to the displacement of the cam member 47, the rack bar 52 is displaced downward in FIG. As a result, the rotation direction of the planetary gear mechanism 41 and the displacement direction of the relay rod 31 are opposite to those in the above case, and the left and right rear wheels RW1,
RW2 is steered relatively to the left, that is, in opposite phase to the left and right front wheels FW1 and FW2.

In this way, when the left and right front wheels FW1 and FW2 are steered to a large steering angle, the left and right rear wheels RW1 and RW2 are steered to have a relatively large steering angle in opposite phase to the left and right front wheels FW1 and FW2. The turning performance of the vehicle at low speed is improved. In this case, the relay rod 31 in the rear wheel steering device B is connected to the control valve 3
6, planetary gear mechanism 41, rack bar 52, cam member 4
Since it is mechanically connected to the relay rod 14 in the front wheel steering mechanism A via the cable 42, etc., the left and right rear wheels RW1, RW
2 is not steered independently of the left and right front wheels FW1 and FW2, and the running safety of the vehicle is ensured. The cable 42
Has some expansion and contraction and play in the connecting portion, and the displacement of the relay rod 14 in the front wheel steering mechanism A is not accurately transmitted to the relay rod 31 in the rear wheel steering device B.
In this case, since the displacement amount of both rods 14 and 31 is large, the error rate does not become so large, and there is no hindrance to the steering of the left and right rear wheels RW1 and RW2.

Next, a case where the left and right front wheels FW1 and FW2 are steered to a relatively small steering angle will be described. When the steering wheel 11 is turned slightly, the turning is transmitted to the relay rod 14 as described above, and the left and right front wheels FW1 and FW2 are steered in the turning direction of the steering wheel 11 at a small steering angle.

In such a case, since the displacement amount of the relay rod 14 transmitted via the cable 42 is small, the displacement amount of the cam member 47 in the front-rear direction is also small. Since there is a dead zone in the center of the cam member 47 and the rack bar 52 is kept in the neutral position, the sun gear 41a is fixed. On the other hand, at this time, the electric control circuit 65
Calculates the target rear wheel steering angle δr * defined by the above formula based on the detection signals from the various sensors 61 to 64, and the steering angles of the left and right rear wheels RW1, RW2 are calculated as the target rear wheel steering angle δ.
The rotation of the electric motor 66 is controlled to be r *, and the motor 66 cooperates with the power cylinder 37 to displace the relay rod 31 via the worm gear 67, the ring gear 41b, the planetary gears 41c and 41c, and the control valve 36. Control, so
The left and right rear wheels RW1 and RW2 are steered to the target rear wheel steering angle δr * according to the displacement of the relay rod 31. Then, the steering angle ratio coefficients K ₁ (V), K ₂ (V), K ₃ (V) for determining the target rear wheel steering angle δr * by the electric control circuit 65 and other variables δf,
δf / δt, Y represents the running state of the vehicle and is a variable for steering the left and right rear wheels RW1, RW2 in phase with the left and right front wheels FW1, FW2 as described above. Are steered in phase with the left and right front wheels FW1 and FW2 according to the running state of the vehicle.

In this way, when the left and right front wheels FW1 and FW2 are in a small steering angle, the electric control circuit 65 and the electric motor 66 do not use the cable 42 that has an error due to expansion and contraction and looseness of the connecting portion.
Since the RW2 is steered, the left and right rear wheels RW1 and RW2 are accurately and subtly controlled according to the running state of the vehicle without any error, and the small steering angle steering is performed accurately at high speeds to improve the running stability of the vehicle. . Further, during steering control by the electric motor 66,
The rotation of the gear 41b is limited to a small range by the engagement of the step portion 41b2 provided on the ring gear 41b and the protrusion 41d, so that even if a failure occurs in the electrical system such as the various sensors 61 to 64, the left and right The rear wheels RW1 and RW2 are limited within the small steering angle range corresponding to the above range, and the traveling safety of the vehicle is ensured. Furthermore, in response to the abnormalities of the various sensors 61 to 64, the electric control circuit 65
Even when the left and right rear wheels RW1 and RW2 are stopped from being steered, the steering control by the first drive means is performed according to the displacement transmitted via the cable 42, so that the small turn at low speed traveling is performed. Performance is secured, and it is possible to partially exhibit the function of the vehicle as a front and rear wheel steering vehicle.

Further, according to the above-mentioned embodiment, when the steering control system of the left and right rear wheels RW1, RW2 is not controlled due to a failure of the steering control system of the left and right rear wheels RW1, RW2, the relay rod is actuated by the action of the neutral return mechanism including the spring 71. Since 31 is returned to the neutral state,
In such a case, the left and right rear wheels RW1 and RW2 are maintained in the neutral state, and the safety of the vehicle is sufficiently ensured.

In the above embodiment, the cam surface 47a is formed on one side surface of the cam member 47, and the copying roller 53 is moved along the cam surface 47a. However, as shown in FIG. Even if the above embodiment is modified, a cam groove 47b is formed on the upper surface of the member 47, and the copying roller 53 is fitted in the cam groove 47b to move the roller 53 along the groove 47b. Good. Further, the copying roller 53 of the above-described embodiments and modified examples may be configured with an engaging member such as a pin that moves along the cam surface 47a or the cam groove 47b.

In the above embodiment, the push-pull cable 42 is used as the connecting member for transmitting the displacement of the relay rod 14 in the front wheel steering mechanism A to the rear part of the vehicle body.
Instead of the above, two cables that are only pulled (pulled) may be used, or a connecting member in which a large number of connecting elements are connected by a large number of joints may be used. In short, a non-stretchable flexible member capable of transmitting the displacement in the front wheel steering mechanism A may be used as the connecting member even if it includes some transmission displacement error.

In the above embodiment, when the left and right rear wheels RW1 and RW2 are electrically steered within a relatively small steering angle, the above equation δr * = K ₁ (V) · δf + K ₂ (V) · δf / δt + K
_Although the steering angles of the rear wheels RW1 and RW2 are set based on ₃ (V) · Y, this is merely an example, and any term in the above formula may be deleted. The same applicant as previously filed Japanese Patent Application No. 61-219015 (rear wheel steering control device for front and rear wheel steering vehicles) to detect the slip state of each wheel, or As disclosed in Japanese Unexamined Patent Publication No. 60974 (vehicle steering device), the lateral acceleration of the vehicle is detected, and the steering value of the left and right rear wheels RW1 and RW2 is controlled by considering the control value based on the detection result in the above equation. You may

Further, in the above embodiment, the rotation of the pinion shaft 55 and the rotation of the rotating shaft 66a of the electric motor 66 transmitted from the front wheel steering mechanism A via the cable 42, the cam member 47 and the rack bar 52 are controlled by the planetary gear mechanism 41. Although the input shaft 36b of the control valve 36 is transmitted via the planetary gear mechanism 41, the rotation of the pinion shaft 55 and the rotating shaft 66a may be directly transmitted to the input shaft 36b of the control valve 36. Good. In such a case, the input shaft 36b of the control valve 36, that is, the rotating shaft 66a of the electric motor 66 is directly driven according to the rotation of the pinion shaft 55.

In addition, in the above-described embodiment, the second electric motor 66, etc.
When the relay rod 31 in the rear wheel steering device B is driven by this driving means, the step portion 41b2 of the ring gear 41b and the projection portion 41d.
The means for limiting the steering range of the left and right rear wheels RW1, RW2 by engaging with and locking the left and right rear wheels RW1, RW2 in the neutral state was not specifically exemplified, but the same applicant as the present application As disclosed in Japanese Patent Application No. 61-139248 (rear wheel steering control device for front-rear wheel steering vehicle) filed earlier by the applicant, a steering control device that is electrically and hydraulically controlled is used to control the control valve 36. The rotation of the output shaft 36a may be limited within a predetermined range, and the rotation of the coaxial shaft 36a may be prohibited.

Furthermore, in the above embodiment, the relay rod 31 is driven and controlled by the hydraulic pressure of the power cylinder 37,
If the relay rod 31 can be driven by the rotational force of the electric motor 66, the applicant of the present application previously filed Japanese Patent Application No. 62-215782.
No. (rear wheel steering device for front and rear wheel steering vehicles), the relay rod 31 may be driven to steer the left and right rear wheels RW1 and RW2 without utilizing hydraulic pressure. According to this, the control valve 36 and the power cylinder 37 are unnecessary. Further, even if the rotary type control valve 36 is not used as in the above-mentioned embodiment, it can be applied to Japanese Patent Application No. 62-277832 (rear wheel steering device for front and rear wheel steering vehicles) previously filed by the same applicant as the present application. As shown, a spool valve having an axially displaced spool may be used.

[Brief description of drawings]

1 is an overall schematic view of a front and rear wheel steering vehicle equipped with a rear wheel steering system according to an embodiment of the present invention, FIG. 2 is a schematic view showing details of the planetary gear mechanism 41 of FIG. 1, and FIG. 1 is a characteristic diagram showing characteristics of the cam member, FIG. 4 is a characteristic diagram showing characteristics of a steering angle ratio coefficient used in the electric control circuit of FIG. 1, and FIG. 5 is a rear view of FIG. It is a schematic diagram showing a modification of a wheel steering device. Explanation of symbols A: front wheel steering mechanism, B: rear wheel steering device, FW1, FW2 ...
… Front wheels, RW1, RW2 …… Rear wheels, 11 …… Steering wheel, 14,31
...... Relay rod, 36 ...... Control valve, 37 ...... Power cylinder, 41 ...... Planetary gear mechanism, 42 ...... Cable,
47 …… Cam member, 52 …… Rack bar, 53 …… Copying roller, 55 …… Pinion shaft, 61 …… Front wheel steering angle sensor, 62…
… Vehicle speed sensor, 63 …… Yaw rate sensor, 64 …… Rear wheel steering angle sensor, 65 …… Electric control circuit, 66 …… Electric motor.

Claims (1)

(57) [Claims] 1. A power cylinder for generating a steering force for steering a rear wheel by supplying / discharging hydraulic oil, and supplying / discharging hydraulic oil to / from the power cylinder according to a displacement of an input member. A control valve that controls steering in proportion to the amount of displacement from the neutral position of the input member, and a mechanical displacement that is connected to the front wheel steering mechanism at one end and is linked to the steering of the front wheels and that is proportional to the amount of steering of the front wheels. A transmission mechanism that transmits to the end, and a mechanical displacement that is connected to the other end of the transmission mechanism and that is transmitted by the transmission mechanism is input, and the control is performed according to the mechanical displacement in a steering angle range of the front wheels above a predetermined value. A drive mechanism that largely displaces the input member of the valve, an electric actuator that is electrically driven to displace the input member of the control valve within a small range, and a drive mechanism that drives the electric actuator according to the running state of the vehicle. Rear wheel steering apparatus of the front and rear wheel steering vehicle, characterized in that it comprises an electric control circuit for controlling.